The present invention relates, in general, to an exhaust-steam pipeline for a steam power plant.
An exhaust-steam pipeline for a steam power plant, in particular steam turbine, is intended to carry exhaust steam from the outlet of the steam turbine via a main steam line to branch lines by which the exhaust steam is directed to individual condenser elements. This process is executed mainly under vacuum conditions. The exhaust-steam pipeline for an air-cooled condenser normally has a diameter between 1 m and 10 m. The presence of local flow losses have been experienced within the exhaust-steam pipeline as a consequence of a local change in the flow cross section or flow direction. Despite the stepped decrease in the pipeline cross section at the connection zone of the branch line, a pressure drop occurs in conventional exhaust-steam pipelines at the port of the branch line as a result of the exhaust steam flowing freely past this port.
German Pat. Publication No. 1 945 314 discloses an exhaust-steam pipeline which attempts to reduce the pressure drop at the branching points of the branch lines by reducing the pipeline cross section by using two pipe pieces of different diameter which are nested within one another and suitably sealed off whereby the smaller pipe piece is sufficiently pushed into the greater pipe piece to form a ring space and to cover the connection port of the branch line in radial direction in the greater pipe piece. A drawback of this construction is the inability to decrease the pressure drop beyond a certain level. Losses are typically experienced in the area of the connection zones, when the flow of exhaust steam is deflected. These flow losses are in addition to the pressure drops as encountered along the pipeline.
When the main steam line extends horizontally near the bottom, the upwardly extending branch lines-must be constructed long enough. FIG. 1 shows such a prior art exhaust-steam pipeline 1 with a horizontal main steam line 2 and branch lines 3 extending vertically upwards from the main steam line 2. Distribution pipes 30 of unillustrated condenser elements are fluidly connected to the upper ends of the branch lines 3. In this construction, the branch lines 3 are not only very long but must also be appropriately supported along their length dimension. As thermal length fluctuations must be compensated, the provision of compensators in the branch lines 3 is required to position the individual portions of the branch lines 3 at proper orientation on the unillustrated steel framework. This complicates the installation. The overall length of the pipeline is relatively long so that substantial tonnage needs to be transported which in turn also complicates the assembly. Also, accessibility is impeded and requires oftentimes covering of very long distances as any direct path is blocked by the bottom-proximal main steam line 2.
Therefore, it has been proposed to elevate the horizontal main steam line to thereby shorten the individual branch lines, as shown in FIG. 2. While the weight of the branch lines 3 is lighter despite the integration of compensators, this approach requires the integration of at least two 90° bends in the main steam line 1 to conduct the exhaust steam, exiting in horizontal direction, into the vertical length portion, and from there again into a horizontal length portion. These 90° deflections require the installation of guide vane elbows within the bends in order to reduce the drag coefficient. When larger plants are involved, the mass of the elbows becomes very high and can reach 7 to 20 t that needs to be supported. Thus, this great mass no only complicates the assembly but poses also a problem in connection with earthquakes. In view of the great mass of the horizontal length portion of the main steam line including the guide vane elbows in the transition area to the vertical length portion of the main steam line, it is necessary to provide particular support structures in regions that are especially prone to earthquakes in order to absorb vertically acting shocks.
Typically, the use of spring supports 4 is proposed to compensate for heat-triggered length changes to thereby provide a sufficient support of the horizontal length portion of the main steam line. This involves, however, the risk that in the event of vertical shocks caused by an earthquake the spring supports are incapable to absorb the relatively great mass of the main steam line and the guide vane elbow. Thus, there is a need for providing additional dashpots in the form of hydraulic dampers. These dashpots in combination with the springs of the spring supports 4 provide a spring-damper assembly to prevent a propagation of forces triggered by an earthquake from the main steam line 2 to the steam turbine on which the main steam line 2 is, in fact, attached. The spring supports 4 together with the dashpots constitute relatively complicated components which have to be repeatedly installed along the length of the main steam line 2 in order to ensure an even elevating and lowering of the horizontal length portion of the main steam line 2. FIG. 2 shows schematically the further spring supports 4 by way of doubly breached lines.
FIGS. 4 and 5 show further prior art exhaust steam pipelines 12, 13 which essentially correspond to the constructions of FIGS. 1 and 2, with the difference residing in the arrangement of four to twelve branch lines 3 which are respectively connected via transverse branches of the main steam line 14 to a central duct 15. FIG. 5 shows the elevated disposition of the exhaust-steam pipeline 13 with spring supports 4, as described in connection with FIG. 2.
It would be desirable and advantageous to provide an improved exhaust-steam pipeline which obviates prior art shortcomings and which is easy to install while yet keeping a pressure drop to a minimum.